This invention relates to positioning roller assemblies for cold rolling tubes.
During cold rolling, the tube is typically offset angularly from the centerline of grooving roller contact surface so that the tube continuously feeds itself into the grooving machine. It has been known to use a guide roller positioned to the side of the tube to offset the axis of the tube so that the user does not have to manually offset the tube while the tube is being cold rolled.
When cold rolling a groove in a tube, the end of the tube being cold rolled has a tendency to flare. Flaring is increased when the opposite end of the tube angles upward from horizontal. When cold rolling longer tubes, e.g., longer than about 4 or 5 feet, flaring is minimized because the weight of the tube itself prevents it from angling upward.
Large diameter extruded tubes often have a non-uniform wall thickness. The forces applied when roll grooving can vary due to the varying wall thickness, and cause the grooved end of the tube to be off axis from the remainder of the tube.
U.S. Pat. No. 5,778,715, to Lippka et al., the complete disclosure of which is hereby incorporated by reference, discloses a positioning roller assembly for use when cold rolling a tube. The positioning assembly includes two positioning rollers rotatably mounted to a positioning plate and disposed for initial contact with a tube surface. The positioning plate is spring coupled to a support for an outside roller, which acts with an inside roller to shape the tube. This coupling maintains contact of the positioning rollers relative to the tube surface when the outside roller is moved during, e.g., groove rolling. The spring mechanism allows for some small variation in tube thickness, applying an increased load when a thicker portion of tube is passing through the groove rolls, and a reduced load when a thinner section is passing through the groove rolls, which follows the load applied by the outside groove roll.
According to one aspect of the invention, a cold rolling apparatus includes a forming roll which applies a forming load to a tube when cold rolling the tube, and a hydraulic positioning assembly including a positioning roller disposable for initial contact with a tube surface and arranged to apply a positioning load to the tube.
Embodiments of this aspect of the invention may include one or more of the following features.
A hydraulic circuit is coupled to the forming roll, e.g., an outside roll, for applying the forming load to the tube. The hydraulic positioning assembly is coupled to the hydraulic circuit such that the positioning load is related to the forming load. The hydraulic positioning assembly includes a face plate mounted for movement with the forming roll, and the positioning roller is mounted to the face plate. The hydraulic positioning assembly includes a piston and the face plate is coupled to the piston for movement with the piston relative to the forming roll. The piston is housed within a cylinder body coupled to a guide block which is coupled to the forming roll. The cold rolling apparatus includes two positioning rollers.
According to another aspect of the invention, a method of applying a positioning load to a tube during cold rolling includes placing the tube between an inside roll and an outside roll, placing a positioning roller against a surface of the tube, applying a forming load to the tube with the outside roll through a hydraulic circuit, and applying a positioning load to the tube with the positioning roller through the hydraulic circuit such that the positioning load is related to the forming load.
According to another aspect of the invention, a hydraulic assembly for controlling movement of a positioning roller assembly of a cold rolling apparatus includes a hydraulic cylinder body configured for coupling to a forming roll of the cold rolling apparatus for movement therewith, and a piston housed by the cylinder body for movement relative to the cylinder body. The piston is adapted for coupling to the positioning roller. A hydraulic line has a first end coupled to the hydraulic cylinder and a second end coupled to a fitting.
The hydraulic positioning cylinder can be provided as part of a retrofit kit to upgrade existing spring-actuated positioning mechanisms.
The coupling of the hydraulic load to the forming roll and the positioning roller maintains the loads applied to the tube by the forming roll and the positioning roller at a constant ratio, even during rolling of tubes of uneven thickness. This advantageously reduces the tendency of tubes of uneven thickness to form off-axis ends.
Other advantages and benefits of the present invention will be apparent from the following detailed description and the accompanying drawings.